Federal officials have identified three “hot spots” of intense contamination — and the source of cancer-causing toxic vapors — along the polluted Gowanus Canal.

The officials remained mum last week about what risks the gunk poses to humans and animals — but they did reveal that an astonishing 90 percent of pollutants in the canal originate from just three sites along the 1.8-mile waterway.

The terrible trio mirrors locations where gas plants once stood: Metropolitan Works, at 12th Street and the canal; Fulton Municipal Works, at Degraw Street and Third Avenue; and Citizens Gas Company, at Smith and Fifth streets.

From the 1860s to the late 1950s, the companies literally helped fuel the Industrial Revolution — but in the process, generated a by-product called coal tar, a substance containing an array of hazardous compounds.

The foul tar has since seeped deep underground, where it continues to migrate into the fetid waterway, its presence confirmed by an oily surface sheen. The tar can also be gasified, producing cancer-causing vapors.

The agency is sifting through a mountain of data it collected since the canal was named a Superfund site last March, a recognition of its status as one of the nation’s most polluted waterways. Once that work is completed, said Walter Mugdan, a regional director with the Environmental Protection Agency, officials will “determine what to do to clean it” — a process that will take 10 to 12 years, and cost $500 million.

Those living and working near the canal said they are anxious for a clean-up.

“Yes, we are concerned, but we are more concerned about the big picture,” said Beth Leonard, an administrator at Spoke the Hub Dancing Company, which has a studio on Douglass Street, near the Fulton site. “We have the highest hope that the canal is developed and turned into a place that fulfills its potential.”

Longtime Gowanus resident Linda Mariano is also taking a macro view.

“It’s not just isolated toxins — it’s the whole package!” she insisted. “We’ve had health concerns for years.”

Still, she said, she’s not planning on moving any time soon. “We’re diehards. We want to see it through. We want to see it fixed.”

But not everyone is alarmed.

“I didn’t feel as though we were threatened at all by the canal,” said Zaleena Ishmael, who once owned the Stratford Manor, a bed and breakfast on 10th Street, near the Metropolitan site. “The biggest problem here is the train that makes noise.”

The state Department of Environmental Conservation is overseeing the clean-up of the land at all three sites. The agency did not return a call for comment.

Energy giant National Grid is on the hook for all three clean-ups, as it bought out the companies who once lined, and illuminated the canal. The company is in the midst of its own investigatory work at all three sites.